The present invention relates to a liquid crystal display device having a high picture quality and in which residual image is substantially eliminated.
In a conventional liquid crystal display device, two facing transparent electrodes formed respectively on each of two substrates are used as the electrodes for driving the liquid crystal layer. In such a device, a display method represented by a twisted nematic display has been adopted, wherein the crystal display operates by being supplied with an electric field having approximately a vertical direction to the substrate boundary planes. On the other hand, in arrangements wherein the electric field has approximately a parallel direction to the substrates, methods utilizing a pair of comb-like electrodes are disclosed, for example, in JP-B-63-21907 and WO91/10936. In these cases, the electrodes are not necessarily transparent, since opaque metallic electrodes having high conductivity are used. However, the above-mentioned publications do not provide any teachings concerning liquid crystal material, oriented film and insulating film, which are necessary for obtaining high picture quality when driving the display system, in which the electric field is supplied to the liquid crystal in an approximately parallel direction to the substrate plane (hereinafter referred to as an in-plane switching system), with an active matrix driving method or a simple matrix driving method.
When a character or a drawing is displayed in a display plane, an image of the character or the drawing remains for a while in the display plane even after erasing, and sometimes it causes an uneven display known as an afterimage. The afterimage is a common problem which causes deterioration of image quality for both the display method wherein the electric field is supplied in a perpendicular direction and the display method involving the in-plane switching system. Especially, in case of the in-plane switching system, the afterimage is generated more easily than the case wherein the electric field is generated perpendicularly to the substrate plane.